<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>elementContains</title>
</head>

<body>
    <div>打开浏览器控制台查看结果</div>
    <script>
        const elementContains = (parent, child) =>
            parent !== child && parent.contains(child);
        console.log(elementContains(
            document.querySelector('head'),
            document.querySelector('title')
        ));;
        // true
        console.log(elementContains(document.querySelector('body'), document.querySelector('body')));
    </script>
</body>

</html>